Conventionally, to perform a medical examination on intervertebral discs by using an MRI apparatus, a slice image parallel to an intervertebral disc and including the intervertebral disc are taken. To perform such a medical examination, for example, a method is known by which an MRI apparatus automatically detects intervertebral discs from a detection-purpose image on which the spine of a subject is visualized and determines positions of imaging slices with respect to the detected intervertebral discs. Another method is also known by which vertebral bodies are similarly detected, so that positions of imaging slices are determined with respect to the detected vertebral bodies. When a medical examination is performed by using either of these methods, there are some situations where the detection of the intervertebral discs or the vertebral bodies fails in a region where the contrast of the intervertebral discs or the vertebral bodies is weak on the detection-purpose image.